1. Field of the Invention
The present invention relates to a technology for displaying a computerized tomography (CT) image and, in particular, to a medical image processing system and method for evaluating the rate of a narrowing of a coronary and/or a characteristic of a blood vessel by defining a plane to project a CT-image to be displayed.
2. Description of the Related Art
An interventional Radiology-computerized tomography (IVR-CT) apparatus has been proposed which has a combination of an X-ray CT apparatus and a radiographic X-ray apparatus including a C-arm, which is a substantially C-shaped supporting device.
The X-ray CT apparatus includes a CT base (gantry) having a hollow part around which an X-ray generating source and an X-ray detector are provided. A subject (patient) mounted on a table-top is introduced into the hollow part, and X-ray transmission information (projection data) in directions on the subject is by rotating the X-ray generating source and the X-ray detector around the hollow part. Based on the information, a tomographic image is reconstructed.
On the other hand, the radiographic X-ray apparatus performs radiographic X-ray by using an X-ray generating source at one end of the C-arm and an image intensifier (I.I.) functioning as an X-ray detecting device at the other end. In particular, the radiographic X-ray apparatus is used for the purposes of angiography within the subject. This is also generally called an angio apparatus. The angio apparatus allows the simultaneous implementation of the operation of insertion of a catheter into (that is, operation or examination by a doctor on) a subject and radiographic X-ray in parallel.
The IVR-CT apparatus allows the operation or positioning of the CT gantry in the X-ray CT apparatus and the C-arm in the angio apparatus provided in parallel within one space. For example, based on information on the subject, which is obtained by one apparatus, how an examination is to be performed in the other apparatus may be determined, and the examination may be carried out after a shorter period of time.
Currently, a visual blood vessel evaluations are performed based on a curved multi planer reconstruction (CPR) image, a minor axis image (horizontal section image) or a volume rendering (VR) image along blood vessel ramifications (blood vessel lining membrane) extracted from CT reconstruction data. The display of an image projecting a curved plane included in a blood vessel lining membrane has been proposed as display allowing the easy diagnosis, which is closer to the senses of an observer. For the diagnosis of the heart, the image display may be more effective with the display in the same direction of the projection (direction of vision of an observer) as the imaging direction in the coronary angiography.
In order to perform the evaluation on a characteristic of blood vessels such as the evaluation of the rate of a narrowing on a CT-image, the display of the CT-image in the same direction of the projection (direction of vision of an observer) as the direction of imaging of an angio-image thereof is effective. However, the strict reproduction of the same direction of the projection as the direction of the imaging of the angio-image on the CT-image is difficult because of the difference in modality or since the generation of CT-images in the same heartbeat phase timing as that of angio-images is difficult.
An optimum direction of imaging of the angio-image is defined by irradiating X-rays to a subject in the operation of a percutaneous coronary intervention (PCI), which is a method for extending a coronary narrowed by arteriosclerosis by using a catheter. However, the definition (search) of the direction of imaging of the angio-image takes time, and a subject may be exposed to X-rays, which is a problem. The amount of exposure to X-rays is desirably reduced by defining the disease part and an optimum direction of imaging of the angio-image by using a pre-shot CT-image. However, the reproduction of the direction of imaging of the angio-image in coronary angiography from the direction of display of the CT-image is difficult unless the projected image of the target vessel is only used.